杭电 2034 ( 人见人爱A-B ) java

import java.util.ArrayList;
import java.util.Scanner;

public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
while(sc.hasNext()){
int n = sc.nextInt();
int m = sc.nextInt();
if (n == 0 && m == 0) {
break;
}
ArrayList<Object> list1 = new ArrayList<>();
for (int i = 0; i < n; i++) {
list1.add(sc.nextInt());
}
ArrayList<Object> list2 = new ArrayList<>();
for (int i = 0; i < m; i++) {
list2.add(sc.nextInt());
}
list2.retainAll(list1);
list1.removeAll(list2);
if (list1.isEmpty()) {
System.out.println("NULL");
}else {
Object[] arr = list1.toArray();
int[] arr1 = new int[arr.length];
for (int i = 0; i <= arr.length - 1; i++) {
arr1[i] = (int)arr[i];
}
selectSort(arr1);
for (int i = 0; i < arr1.length; i++) {
System.out.print(arr1[i] + " ");
}
System.out.println();
}
}
}

public static void selectSort(int[] arr) {
for (int i = 0; i < arr.length - 1; i++) {
for (int j = i + 1; j < arr.length; j++) {
if (arr[i] > arr[j]) {
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
}
}